1. Field of the Invention
The present invention relates to an accelerometer of the kind comprising a support, an inertial mass connected to the support by a hinge means, and an elongate vibrating element whose ends are respectively connected to the inertial mass and to the support.
2. Description of the Prior Art
This type of accelerometer, described for example in U.S. Pat. No. 4,517,841 has the advantage of delivering information easy to put into digital form.
This information is the vibration frequency of the vibrating element, or several vibration frequencies in the case of multimode operation, which varies on the one hand as a function of the temperature of this vibrating element and on the other as a function of the longitudinal force applied to said element. This force is the sum of a quantity proportional to the magnitude to be measured, which is the acceleration of the inertial mass, multiplied by its mass, and of a stress of thermal origin dependent on the temperature distribution inside the structure, and on the arrangement of this structure.
At uniform temperature, this stress of thermal origin is due to the difference of the expansion coefficients between the materials forming the support and the vibrating element. The value of this stress depends on the one hand on the angular stiffness of the articulation of the inertial mass on the support and on the other hand on the effective angular stiffness of the vibrating element, generally made from quartz, at the level of the embedment.
It is known to reduce the influence of the temperature of the vibrating element on the accuracy of the measurements by using for example two vibrating elements instead of one, arranged in differential fashion, so that the effects related to the acceleration to be measured are added whereas the effects related to the temperature of the vibrating elements are compensated and cancelled out. Such compensation is described in U.S. Pat. No. 4,517,841 mentioned above as well moreover as in the German application No. 30 38660--although, in this latter case, the transducers used are not elongate vibrating elements but piezoelectric transducers in the form of plates.
Naturally, even if that is not its first aim, such a compensation causes a reduction of the effects of the stress of thermal origin exerted on each vibrating element, in the case where the temperature of the whole of the structure is uniform.
However, under rapidly varying thermal conditions, there appear inside the structure thermal gradients such that the effects of the thermal stresses are very considerable.
The present invention aims at overcoming the above drawbacks by providing, in particular for aeronautic and spatial uses, a reduction of the non compensatable thermal stress and so a reduction of the measurement errors.